fix: raise ValueError for reversed page ranges in expand_page_range

A reversed page range like '5-3' would either raise a confusing
'No valid page numbers or ranges found' error (when it was the only
entry) or silently drop the pages when mixed with valid ranges (e.g.
['1-3', '7-5', '8'] returned [1, 2, 3, 8] instead of raising).

Add an explicit check that start <= end and raise a clear ValueError
with a descriptive message identifying the problematic range.

Also adds three new tests covering:
- reversed range alone raises ValueError
- reversed range mixed with valid ranges raises ValueError (no silent drop)
- equal start and end (e.g. '3-3') is valid and returns [3]

Author: basilalshukaili

haystack/utils/misc.py

@@ -61,8 +61,11 @@ def expand_page_range(page_range: list[str | int]) -> list[int]:
             if not parts[0].isdigit() or not parts[1].isdigit():
                 msg = "range must be a string in the format 'start-end'"
                 raise ValueError(f"Invalid page range: {page} - {msg}")
-            start, end = parts
-            expanded_page_range.extend(range(int(start), int(end) + 1))
+            start, end = int(parts[0]), int(parts[1])
+            if start > end:
+                msg = "start must be less than or equal to end"
+                raise ValueError(f"Invalid page range: '{parts[0]}-{parts[1]}' - {msg}")
+            expanded_page_range.extend(range(start, end + 1))
 
         else:
             msg = "range must be a string in the format 'start-end' or an integer"

releasenotes/notes/fix-expand-page-range-reversed-range-8a3f2d1e4b9c5f7a.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed `expand_page_range` silently dropping pages when a reversed range (e.g. '7-5') appeared
+    alongside valid entries. Mixed inputs like ['1-3', '7-5', '8'] previously returned [1, 2, 3, 8]
+    with no warning, losing pages 5-7. A reversed range now raises `ValueError` with a descriptive
+    message identifying the offending range.

test/utils/test_misc.py

@@ -195,3 +195,16 @@ def test_invalid_string_raises_value_error(self):
     def test_malformed_range_with_multiple_hyphens_raises_value_error(self):
         with pytest.raises(ValueError, match="Invalid page range"):
             expand_page_range(["1-3", "5-10-15"])
+
+    def test_reversed_range_alone_raises_value_error(self):
+        with pytest.raises(ValueError, match="Invalid page range.*start must be less than or equal to end"):
+            expand_page_range(["5-3"])
+
+    def test_reversed_range_mixed_raises_value_error(self):
+        # Previously, a reversed range mixed with valid entries silently dropped the reversed range.
+        # e.g. ["1-3", "7-5", "8"] would return [1, 2, 3, 8], losing pages 5-7 with no error.
+        with pytest.raises(ValueError, match="Invalid page range.*start must be less than or equal to end"):
+            expand_page_range(["1-3", "7-5", "8"])
+
+    def test_equal_start_end_is_valid(self):
+        assert expand_page_range(["3-3"]) == [3]